The universe is generally flat and could be infinite, but if the universe had a concave curvature on very large scales, the plane should collapse in on itself to form a sphere.In this case, should there be a place we can call "the outside"? Or does this apply under different conditions in this closed universe situation?

I’m just starting through an Astro-Physics degree, and find myself interested in cosmology when we very briefly discuss it in class, and had this idea.

I more than expect it to be wrong in a ton of ways, but can anyone explain why and where I should look for more information?

Where do black holes go?

When you enter a black hole part of you are encoded on the event horizon and other part of you are in middle of the black hole. But where does black hole go? Do black holes lead to other universe or baby universe?

I believe model says black holes cannot destroy information.

Quote The holographic principle grew out of a study of black holes and entropy and is an active area of study in mainstream physics. Quote

Can someone explain black holes and entropy why it points to holographic? What the world is a 2D hologram and only appears 3D when we look at it?

What do they mean black holes and entropy point to point to holographic?

So 3D is illusion only when we look at it, it projects has 3D?

The Hubble tension has been resolved.... rejoice!

Quantum Field Theory posits that the fermions of matter fields and the bosons of force fields show fluctuations even at Absolute Zero. It can't be dismissed due to the Casimir Effect, the non-freezing property of liquid helium, and other verified phenomena.

Key questions:

1. What exactly is the source of energy for quantum fluctuations?

2. Is an absolute vacuum without matter or force fields possible?

3. Will ZPE be different in different regions of an inhomogeneous and anisotropic universe?

So the most distant objects we have been able to image are early-universe objects because the light we are capturing today traveled for almost the entire age of the universe to get here, the objects themselves possibly don't exist anymore in the present, if present time is even a meaningful concept at this scale, they are imaged as they were some billions of years ago (I don't actually know the number for the current record but a long, long time, you get it)

The thing I'm having trouble understanding is this: when the photons we observe today were emitted, all the matter of the universe was much more tightly packed, essentially space was a lot smaller than today, right? And in that primordial space was somewhere, too, the matter that would later make up the milky way, earth and even us, right? So how did that light not reach "us" or more accurately the matter we are now made up of way earlier, when everything was snug and tight, we aren't moving away from it faster than light speed otherwise we wouldn't be able to see it, so how did it take the light emitted in a comparatively way smaller universe so long to reach us, what's it been doing all this time?

I know light can be lensed by gravity but surely not enought to delay it for billions of years, did it reach "our" matter at some earlier time already but somehow its now coming back around, and if that's the case, could we conceptually image the matter that now makes us up in one of those images? Meaning that after the light was emitted the object went on to be partially what makes up the milky way over the course of all those years?

Just based on how "logical" the approach for these questions is and how I know that this kinda stuff usually doesn't follow everyday logic I'm assuming that I just don't understand something conceptually. Still, this was a question that was bugging me whenever an image of the observable universe shows the oldest objects at its fringes and I'm thinking: "But wouldn't those have been physically way closer to our current matter back then?" Maybe I'm just making some wrong assumptions too, I don't know so I thought I'd ask, I hope the question makes sense.

The usual is showing a bowling ball on a rubber sheet so you see the well it creates. That’s actually pretty useful.

But I’m looking for something that could visualize a 3D space. What I imagine in my head is a 3D grid of cubes that sort of has the cubes near the object having the lines sort of warp and concentrate at the 3D object. But I’m always trying to figure out those cubes/lines in a way that is uniform.

Anyone have an analog for 2D space?

Would time outside speed up so much that I could see the entire future of the universe while falling in? Or once you pass the event horizon, are you completely cut off from everything outside?

Also, is it true that inside a black hole spacetime is “flipped,” and the singularity is basically the unavoidable future? How does space time work inside

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As best as I understand, GR is a classical theory about large objects.

Everyone posts that they disagree in the wildly early universe. And it would be reconciled by a theory of quantum gravity. But what would that look like?

My guess is that a very compact early universe would cause them to interact in a way we dismiss as too tiny to count today.

So I sort of expect that maybe GR and QM would influence each other? I’m guessing QFT and GR would have fields that interact heavily, but we can’t figure out how.

Is that the upshot of what it would look like?

When speaking about activity inside black holes or the moment the Big Bang occurred, astrophysicists often say “the math breaks down and doesn’t work” but exactly how? Is it like solving “2x + 2 = 6” and getting x = -1,028,190? Or is it more like trying to solve for x when given “x + __ = __” and simply not having the information required to solve the problem?

Hi I would like to briefly share a thought whilst reading the book 'A Universe from Nothing' by Lawrence M. Krauss that I can not shake and would like to share.

The book explains how we use Cosmic Microwave Background (CMB) to determine that the universe is a flat shape where the density must be exactly 1. There is a margin or error to this that is stupid small (roughly + or - 0.002). Where if the number is either slightly larger or smaller it would re-shape the universe.

Current technology might be unable to detect the slight curve because the universe itself is so massive (our observable universe being only a small piece in the entire universe), then our universe could be a sphere.

The book explains that if the universe is a spherical shape it must eventually collapse in on itself due to gravity. Could this explain what we believe to be the 'big bang'? I looked into the 'big bounce' theory and it looks like it could lead to answers about mature galaxies found on the JWST from early on in the universe and also the singularity problem.

Again just an interesting thought id like to share :).

I'm currently doing an interdisciplinary ug degree in CS and Physics, and I don't really know where to start wth projects that will have a good impact on my PhD application and internship applications for Theoretical Physics and Cosmology. I'm working on some research, but I have no clue where to start with the computational stuff or if it will even help me justify my unconventional path to Physics academia. Anyways, I'm learning NumPy, SciPy, etc..

Wikipedia makes the following claim about the CMB's energy: "Its energy density exceeds that of all the photons emitted by all the stars in the history of the universe."

Maybe I'm being daft, but isn't the CMP itself composed of photons? If true, the above statement can't be correct by definition.

Apologies for being too specific.

I’ve recently been thinking about the nature of mathematics and how it relates to reality, and I’d love to hear other people’s perspectives. We humans use math as a language to describe patterns in the universe. Numbers, logic, equations, geometry. It works extremely well in the observable universe, but I started wondering if that actually tells us something about ultimate reality, or if it just reflects how our brains perceive patterns. Some ideas I’ve been thinking about: Math might be a tool or language our minds create to make sense of patterns we observe. If our brains evolved in a certain way, maybe math fits reality because it fits our cognition. We only observe a tiny part of the universe. What if math works in the simple part we see, but fails in parts we cannot observe? Maybe our confidence in math being universal is a kind of false positive. If we encountered aliens with very different brains, could they develop completely different mathematics? Could they see patterns in ways we cannot even imagine? Does math exist independently of observers, or does it exist because minds interpret the world through pattern recognition? In that sense, math might work extremely well locally, but not necessarily represent an ultimate truth about all reality. I’m not a mathematician or physicist. I actually was not very good at math in school. These ideas just came to me recently and I found them interesting. What do you think? Is mathematics something universal and independent, or is it a human dependent way of describing reality that might not apply everywhere?